U.S. patent application number 10/514461 was filed with the patent office on 2005-09-29 for method for fixing a semiconductor chip in a plastic housing body, optoelectronic semiconductor component.
Invention is credited to Bogner, Georg, Hiegler, Michael, Waitl, Gunter, Winter, Matthias.
Application Number | 20050214968 10/514461 |
Document ID | / |
Family ID | 29285481 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050214968 |
Kind Code |
A1 |
Waitl, Gunter ; et
al. |
September 29, 2005 |
Method for fixing a semiconductor chip in a plastic housing body,
optoelectronic semiconductor component
Abstract
A radiation-emitting or -receiving semiconductor chip 9 is
soft-soldered for mounting on a leadframe 2 over which a
prefabricated plastic encapsulant 5, a so-called premolded package,
is injection-molded. Through the use of a low-melting solder 3
applied in a layer thickness of less than 10 .mu.m, the soldering
process can be carried out largely without thermal damage to the
plastic encapsulant 5.
Inventors: |
Waitl, Gunter; (Regensburg,
DE) ; Bogner, Georg; (Lappersdorf, DE) ;
Hiegler, Michael; (Regensburg, DE) ; Winter,
Matthias; (Regensburg, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
29285481 |
Appl. No.: |
10/514461 |
Filed: |
May 20, 2005 |
PCT Filed: |
May 14, 2004 |
PCT NO: |
PCT/DE03/01557 |
Current U.S.
Class: |
438/106 ;
257/E21.5; 257/E21.51 |
Current CPC
Class: |
H01L 2224/2908 20130101;
H01L 2224/29111 20130101; H01L 2224/48091 20130101; H01L 2224/48247
20130101; H01L 2924/01079 20130101; H01L 2224/32245 20130101; H01L
2924/01075 20130101; H01L 2924/0105 20130101; H01L 2924/014
20130101; H01L 2224/48091 20130101; H01L 2224/29101 20130101; H01L
2224/48247 20130101; H01L 2224/29199 20130101; H01L 2924/0105
20130101; H01L 2924/00 20130101; H01L 2924/01047 20130101; H01L
2924/00014 20130101; H01L 2924/01049 20130101; H01L 2224/29099
20130101; H01L 2924/00014 20130101; H01L 2924/01082 20130101; H01L
2924/00013 20130101; H01L 2224/29111 20130101; H01L 2224/48465
20130101; H01L 24/73 20130101; H01L 2924/0132 20130101; H01L
2924/157 20130101; H01L 2924/00013 20130101; H01L 2224/29139
20130101; H01L 2924/19043 20130101; H01L 2224/29111 20130101; H01L
2924/0132 20130101; H01L 2924/00014 20130101; H01L 2924/01082
20130101; H01L 2224/2929 20130101; H01L 2924/014 20130101; H01L
2924/01047 20130101; H01L 2924/00 20130101; H01L 2224/48247
20130101; H01L 2924/01029 20130101; H01L 2224/48247 20130101; H01L
2224/29111 20130101; H01L 24/83 20130101; H01L 2224/73265 20130101;
H01L 2224/29139 20130101; H01L 33/62 20130101; H01L 24/29 20130101;
H01L 2224/48465 20130101; H01L 2924/01322 20130101; H01L 21/52
20130101; H01L 2224/48465 20130101; H01L 2924/01063 20130101; H01L
2224/29101 20130101; H01L 2224/8319 20130101; H01L 2924/01082
20130101; H01L 2924/0132 20130101; H01L 2224/29007 20130101; H01L
2224/83801 20130101; H01L 2924/01005 20130101; H01L 2924/01006
20130101; H01L 2924/01078 20130101; H01L 2924/12041 20130101; H01L
2924/0132 20130101; H01L 2924/0132 20130101; H01L 2924/00013
20130101; H01L 2924/01047 20130101; H01L 2224/48463 20130101; H01L
2224/73265 20130101; H01L 24/32 20130101; H01L 2924/07811 20130101;
H01L 2224/29111 20130101; H01L 2924/00013 20130101; H01L 2224/29
20130101; H01L 2224/48465 20130101; H01L 2924/01033 20130101; H01L
2224/32245 20130101; H01L 2224/29299 20130101; H01L 2924/00014
20130101; H01L 2924/0105 20130101; H01L 2924/01029 20130101; H01L
2924/0105 20130101; H01L 2224/48091 20130101; H01L 2924/00012
20130101; H01L 2924/01082 20130101; H01L 2924/00012 20130101; H01L
2924/00012 20130101; H01L 2924/00014 20130101; H01L 2924/00014
20130101; H01L 2924/00 20130101; H01L 2924/00013 20130101 |
Class at
Publication: |
438/106 |
International
Class: |
H01L 021/50 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2002 |
DE |
102 21 587.9 |
Claims
1. A method for mounting a semiconductor chip on a thermally and/or
electrically conductive connector arranged in or on a plastic
encapsulant, wherein the connection is produced by means of a soft
soldering process.
2. The method of claim 1, wherein said connector has a first and a
second main surface.
3. The method of claim 2, wherein said first and second main
surfaces are enveloped by said plastic encapsulant.
4. The method of claim 1, wherein said plastic encapsulant contains
a thermoplast.
5. The method of claim 1, wherein said plastic encapsulant contains
a duroplast.
6. The method of claim 1, wherein said plastic encapsulant is
produced by being molded over, particularly injection-molded or
compression-molded over, a leadframe and said connector is part of
said leadframe.
7. The method of claim 1, wherein said connector is a metallization
layer applied to a plastic encapsulant.
8. The method of claim 1, wherein said connector is a heat sink
embedded in said plastic encapsulant.
9. The method of claim 1, wherein a solder layer having a thickness
of between 1 .mu.m inclusive and 10 .mu.m inclusive is used between
said semiconductor chip and said connector.
10. The method of claim 1, wherein a solder layer having a
thickness of between 2 .mu.m inclusive and 5 .mu.m inclusive is
used between said semiconductor chip and said connector.
11. The method of claim 1, wherein said soft-soldering process
takes place at a temperature of between 200.degree. C. inclusive
and 260.degree. C. inclusive.
12. The method of claim 1, wherein the solder material used is
composed substantially of pure tin or of an alloy whose principal
component is tin.
13. The method of claim 1, wherein the solder material used is
composed substantially of an alloy whose material system has a
eutectic composition.
14. The method of claim 13, wherein the solder material used is at
least one alloy from the group of alloys consisting of AgSn, CuSn,
PbSn and InPb or a mixture or layer sequence composed of least two
of said alloys.
15. The method of claim 1, wherein solder material is applied to
said chip before soldering.
16. The method of claim 1, wherein solder material is applied to
said connector before soldering.
17. The method of claim 13, wherein layers composed of different
alloy components of the solder are applied to said semiconductor
chip and/or to said connector.
18. The method of claim 1, wherein a gold film is deposited on said
solder material before soldering.
19. The method of claim 1, wherein said semiconductor chip is
attached to said connector with flux before soldering.
20. The method of claim 1, wherein said semiconductor chip is
attached to said connector with solder paste before soldering.
21. The method of claim 1, wherein a through-type furnace is used
for the soldering operation.
22. The method of claim 1, wherein a heating plate is used for the
soldering operation.
23. The method of claim 1, wherein said plastic encapsulant passes
through a washing unit after the soldering operation.
24. An optoelectronic semiconductor component comprising a
radiation-emitting and/or a radiation-receiving semiconductor chip
on a thermally and/or electrically conductive connector arranged in
or on a plastic encapsulant, wherein a connecting layer between
said semiconductor chip and said connector comprises a soft
solder.
25. The optoelectronic semiconductor component of claim 24, wherein
said connector has a first and a second main surface.
26. The optoelectronic semiconductor component of claim 25, wherein
said first and second main surfaces are enveloped by said plastic
encapsulant.
27. The optoelectronic semiconductor element of claim 24, wherein
said plastic encapsulant contains a thermoplast.
28. The optoelectronic semiconductor component of claim 24, wherein
said plastic encapsulant contains a duroplast.
29. The optoelectronic semiconductor component of claim 24, wherein
said connector is part of a leadframe that is molded over with said
plastic encapsulant, particularly by injection molding or
compression molding.
30. The optoelectronic semiconductor component of claim 28, wherein
said connector is a metallization layer applied to said plastic
encapsulant.
31. The optoelectronic semiconductor component of claim 28, wherein
said connector is a heat sink embedded in said plastic
encapsulant.
32. The optoelectronic semiconductor component of claim 28, wherein
a solder layer having a thickness of between 0.1 .mu.m inclusive
and 10 .mu.m inclusive is provided between said semiconductor chip
and said connector.
33. The optoelectronic semiconductor component of claim 28, wherein
a solder layer having a thickness of between 0.1 .mu.m inclusive
and 5 .mu.m inclusive is provided between said semiconductor chip
and said connector.
34. The optoelectronic semiconductor component of claim 27, wherein
said solder material is composed substantially of pure tin or of an
alloy whose principal component is tin.
35. The optoelectronic semiconductor component of claim 28, wherein
the solder material used is substantially an alloy whose material
system has a eutectic composition.
36. The optoelectronic semiconductor component of claim 35, wherein
said solder material is substantially an alloy from the group
consisting of AgSn, CuSn, PbSn and InPb or a mixture or layer
sequence composed of at least two of said alloys.
37. The optoelectronic semiconductor component of claim 28, wherein
said semiconductor chip is attached to said connector in a
flip-chip assembly, so that an active epitaxial layer sequence
faces said connector.
38. The optoelectronic semiconductor component of claim 37, wherein
said solder layer and a contact layer, particularly a contact
metallization of said epitaxial layer sequence, are all that is
present between said epitaxial layer sequence and said
connector.
39. A method for the production of an optoelectronic component of
claim 37, wherein the method steps of: a) producing said epitaxial
layer sequence on a substrate wafer, b) producing the contact
layer, c) separating the wafers produced in steps a) and b) into
individual semiconductor chips and d) attaching said chips to their
connectors in said plastic encapsulant by soft soldering.
Description
[0001] The invention concerns a method as defined in the preamble
to Claim 1 and an optoelectronic semiconductor component as defined
in the preamble to Claim 24. It further concerns a method for the
production of such an optoelectronic semiconductor component.
[0002] Radiation-emitting and/or -receiving semiconductor chips are
conventionally attached by a gluing process to so-called
pre-encapsulated leadframes, which are made by molding over a chip
mounting area with a plastic encapsulant.
[0003] In the known package designs the semiconductor chip is
mounted on the leadframe by gluing, since this eliminates the high
temperatures that are necessary for soldering processes and that
can damage the plastic encapsulant.
[0004] Due to the very good electrical and thermal conductivity
required for the connection between the semiconductor chip and the
leadframe, especially in the case of high-electrical-output
components, a metal connection between the chip and the connector
would be preferable over a glued connection. Particularly in the
realm of high-output light-emitting diodes, a very good thermal
connection is crucial in order to carry off the dissipated power
brought in from the package and, where applicable, couple it to an
external heat sink. Because of the above-cited potential for damage
to the package, solder connections have heretofore not been used
between the light-emitting diode (LED) chip and the leadframe in
pre-injection-molded plastic encapsulants.
[0005] The object of the instant invention is to develop a method
of the kind cited at the beginning hereof by which a semiconductor
chip can be attached in a plastic encapsulant by means of a
metallic connection between the chip and the connector, and the
risk of impairing the functional capability of the plastic
encapsulant is simultaneously reduced. A corresponding
optoelectronic component and a method for the production thereof is
further to be provided.
[0006] These objects are achieved by means of a method having the
features of Claim 1, an optoelectronic component having the
features of Claim 24 and a method having the features of Claim
39.
[0007] The use of very small amounts of a low-melting solder
eliminates excessive heating of the metal parts contacted by the
plastic encapsulant, which contains a thermoplast and/or a
duroplast and is preferably made of a thermoplast. Especially
preferred as thermoplasts are high-temperature thermoplasts such as
PPA, polysulfone and LPC (liquid crystal polymer). The thermoplasts
are preferably filled with titanium dioxide, glass fibers, mineral
fillers and similar filler materials. A solder layer is preferably
used that allows the soldering to be performed at temperatures of
between 200 and 260.degree. C. At the same time, the use of soft
solder, as opposed to hard solder, largely prevents warping of the
soldered chip, which can lead to chip damage.
[0008] The connector advantageously has a first and a second main
surface. In a particularly advantageous variant of the method, the
first and second main surfaces are enveloped by the plastic
encapsulant, in which case the first and/or the second main surface
border are directly adjacent the plastic encapsulant.
[0009] The low-melting soft solder used can be pure tin, an alloy
whose principal component is tin, or alloys having a eutectic
composition, such as AgSn, CuSn, PbSn or InPb or a mixture of these
alloys. If an alloy is used as solder, it is advantageous to select
the composition of the alloy so that it is to the greatest possible
extent at the eutectic composition of the two- or multi-material
system concerned, so that the melting point of the alloy is as low
as possible.
[0010] It is advantageous if a thin layer is deposited locally on
the points to be soldered, in a thickness of between 1 and 10
.mu.m. It is particularly advantageous if a layer with a thickness
of between 2 to 5 .mu.m is deposited. This prevents wetting of the
side surfaces of the LED chip on the side facing the leadframe,
which in the case of flip-chip assembly (see below) would easily
cause a short circuit of the active epitaxial layer sequence.
[0011] The thin layers of solder can preferably be deposited by
conventional methods, such as vapor deposition, sputtering,
etc.
[0012] If the solder is deposited on the leadframe, this preferably
takes place before the leadframe is molded over with the plastic
encapsulant.
[0013] It is particularly advantageous if thin layers of the
individual components of an alloy are deposited repeatedly in
alternation. Here again, the total thickness of the layer stack is
advantageously between 1 and 10 .mu.m or 2 and 5 .mu.m.
[0014] The metals of the thin layers intermingle during the
soldering process owing to the short diffusion paths to the
respective adjacent layers. The rapid melting of the solder and
thus the rapid soldering of chip and connector advantageously have
the effect that the plastic encapsulant of the premolded package
need be exposed to an elevated temperature for only a short period
of time, and its functional capability is therefore is largely
unimpaired.
[0015] Because of the short soldering time in combination with the
low temperatures of the soldering process, it is therefore feasible
to solder LED chips to leadframes in premolded packages, that is,
to provide LED chips with metallic connections between the chip and
the connector.
[0016] To prevent an oxide layer from forming on the solder or the
to-be-soldered surfaces while the solder is being heated, it is
advantageous, after depositing the solder on a surface for
soldering, to apply a thin layer of gold to the solder and/or to
the surfaces of the chip and leadframe that are to be soldered.
[0017] Low processing temperatures allow the chip to be soldered
largely without warping.
[0018] The tiny volume of solder used makes it possible in
particular to solder chips with the active epitaxial layer sequence
facing the connector. This so-called "flip-chip" arrangement, also
known as "face-down" or "top-down" assembly, is made feasible only
by virtue of the very small volume of solder according to the
technical teaching of the invention.
[0019] Wetting of the side walls of the chip also occurs in
conventional gluing processes. This is why it is difficult in
flip-chip assembly to mount a chip on a leadframe or another
electrically conductive connector via a gluing process.
[0020] Especially with the use of conventional,
silver-particle-filled conductive adhesives, there is also the
problem that silver particles migrate relatively intensively in an
electric field when moisture is present. This is the case in
particular with infrared sensors and infrared radiators, which need
high voltages to operate. To address this problem, in these cases
gold particles are often used as conductive filler in conventional
schemes.
[0021] In contradistinction to this, the use of soft solder is far
more cost-effective.
[0022] Advantageous improvements and embodiments of the method
according to the invention and the optoelectronic component are
recited in the dependent claims.
[0023] Further advantages and preferred embodiments of the method
of the invention and the optoelectronic component will emerge from
the following embodiment examples described in greater detail in
connection with FIGS. 1 to 8.
[0024] Therein:
[0025] FIG. 1 is a schematic diagram of an optoelectronic component
comprising a chip that is mounted by the method of the
invention,
[0026] FIG. 2 is a schematic diagram of an optoelectronic component
comprising a chip that is flip-chip-mounted by the method of the
invention,
[0027] FIG. 3 is a schematic diagram of an optoelectronic component
comprising a chip that is flip-chip-mounted by a conventional
gluing method,
[0028] FIG. 4 is a schematic diagram of a solder point prepared by
a method according to the invention,
[0029] FIG. 5 is a flow chart illustrating the assembly sequence of
a first embodiment example of the method according to the
invention,
[0030] FIG. 6 is a flow chart illustrating the assembly sequence of
a second embodiment example of the method according to the
invention,
[0031] FIG. 7 is a flow chart illustrating the assembly sequence of
a third embodiment example of the method according to the
invention,
[0032] FIG. 8 is a flow chart illustrating the assembly sequence of
a fourth embodiment example of the method according to the
invention.
[0033] The embodiment example depicted in FIG. 1 comprises a
leadframe 2 around which a plastic encapsulant 5 has been
compression- or injection-molded and which comprises a first and a
second main surface (premolded package). In a recess 6 in this
plastic encapsulant 5 that leads from outside the base encapsulant
to the leadframe 2, an LED chip 9 is attached to a connector 12 of
the metal leadframe 2 by means of a soft solder. The first and
second main surfaces of the leadframe are covered with plastic.
Thus, there is substantially no additional heat sink apart from the
leadframe.
[0034] A metallization layer 22 deposited on plastic encapsulant 5
and comprising a connector 12 can alternatively be provided instead
of the leadframe. As a further alternative, a heat sink embedded in
the plastic encapsulant can serve as the connector. A solder layer
3 between LED chip 9 and connector 12 preferably has a thickness of
between 1 and 10 .mu.m. Especially preferably, the solder layer has
a thickness of between 2 and 5 .mu.m. The soft solder in this
embodiment example is composed substantially of pure tin or of an
alloy whose principal component is tin. The solder material for
soft soldering can also, for example, be an alloy whose material
system has a eutectic composition. Candidates for this purpose are
AgSn, CuSn, PbSn or InPb or a mixture or layer sequence composed of
at least two of these alloys. The plastic encapsulant contains a
thermoplast, preferably a high-temperature thermoplast such as PPA.
Polysulfone or LCPs (liquid crystal polymers) can also be used.
Improved temperature resistance can be achieved by means of filler
materials such as, for example, glass fibers, mineral fillers and
TiO.sub.2. The plastic encapsulant can also, however, contain a
duroplast.
[0035] The second embodiment example, depicted in FIG. 2, differs
from the example just described in that the LED chip 9, in a
flip-chip assembly (see above), is attached to a connector by means
of a soft solder. The connector in this case is a metallization
layer 22 vapor-deposited on the base encapsulant 5, but it can
also, as in the first-cited case, be part of a leadframe. Due to
the minuscule thickness of the solder, it is not pressed out from
under the chip 9. The risk of short-circuiting the epitaxial layer
sequence is greatly reduced.
[0036] If solder layers 3 of very large thicknesses are applied,
however, there is a risk, as illustrated in FIG. 3, that the solder
will be pressed out from under the chip 9 placed on the leadframe
2. This solder wets the connector and the side walls of the chip 9.
If the chip 9 is arranged as a flip chip with its active side 4
toward the leadframe 2, the solder, forming a meniscus 13, causes
an electrical short circuit from connector 12 to chip substrate 1
of chip 9 at epitaxial layer sequence 4.
[0037] FIG. 4 shows a particularly advantageous option for the
arrangement of a solder layer (3) which during the soldering
process forms an alloy whose material system has a eutectic
composition. Thin layers (23, 33) of the individual components of
the alloy are arranged alternatingly between the chip and the
connector. Layers (23) are composed, for example, of tin and layers
(33) of silver.
[0038] Due to the short diffusion paths to the respective adjacent
layers, the individual metals intermingle during the soldering
process and form an alloy.
[0039] The embodiment example illustrated schematically in FIG. 5
concerns a mounting sequence for soft-soldering an LED chip in a
premolded package as described exemplarily in the embodiment
example of FIG. 1. A solder layer (for example having a thickness
of 2 to 5 .mu.m) composed substantially of tin or of an alloy whose
principal component is tin is applied to a connector. The connector
can, for example, be a leadframe, a heat sink embedded in the
plastic encapsulant or a metallization layer deposited on a plastic
encapsulant. In the case of the leadframe, a leadframe can in
particular be embedded without the use of a heat sink, so that a
first and a second main surface of the leadframe are covered with
plastic. Flux is then applied to the solder and the chip is placed
thereon. The premolded package then passes, preferably at 200 to
260.degree. C., through a soldering furnace in which the solder
connection is produced. Subsequently, the premolded package passes
through a washing unit in which the residues, produced mainly by
the flux, are rinsed away.
[0040] The flux is necessary to remove the oxide layer that forms
on the solder and the chip in the through-type furnace and to keep
an oxide layer from developing. To prevent the formation on the
solder of an oxide layer that would sharply lower the quality of
the solder connection, a gold film can also be deposited on the
solder prior to the soldering operation.
[0041] As an alternative to the procedure described above, the
solder layer can be deposited on the leadframe before the
production of the plastic encapsulation.
[0042] The process according to the second embodiment example,
which is illustrated schematically in FIG. 6, differs from the
foregoing embodiment example essentially in that solder is used in
the form of a solder paste. The solder paste can be applied to the
connector alone or to the semiconductor chip alone or to both the
connector and the semiconductor chip. An LED chip is placed at the
connector site, which has been prepared with solder paste, inside a
premolded package before the strip passes through the solder
furnace.
[0043] To remove the chemicals such as flux that are present in the
solder paste, a washing unit is also installed downstream of the
soldering furnace in this embodiment example.
[0044] In the method according to the embodiment example of FIG. 7,
the solder is applied to the back side of an LED chip by vapor
deposition. The solder material used is an alloy whose material
system has a eutectic composition. This alloy can be AgSn, CuSn,
PbSn, InPb or a mixture of at least two of these alloys. A layer
sequence of individual alloys or of individual metals forming these
alloys can also be used. The chip is placed on a leadframe inside a
premolded package. In contrast to the preceding embodiment example,
here the leadframe and the chip are heated by means of a heating
plate located under the leadframe in order to melt the soft
solder.
[0045] Here the soldering is performed without the use of a flux.
Consequently, there is no washing unit after the soldering furnace.
The soldered semiconductor component 7 is thereby obtained largely
without impurities in a particularly frugal manner.
[0046] In the method according to the embodiment example of FIG. 8,
as in the previously described embodiment example, an LED chip with
solder vapor-deposited thereon is placed on the leadframe inside a
premolded package. After vapor deposition, the solder layer has a
thickness of between 1 and 10 .mu.m, preferably between 1 and 5
.mu.m. The plastic encapsulation can be produced on the leadframe
by injection molding or compression molding or another molding
process for duroplasts or thermoplasts. In this embodiment example,
flux is first deposited at the location on the leadframe that is to
be soldered. The strip passes through a soldering furnace and then
a washing unit. After the soldering operation, the thickness of the
solder layer is between 0.1 and 10 .mu.m, preferably between 0.1
and 5 .mu.m.
[0047] In all the embodiment examples for the method of the
invention, the LED chip can also be attached to the connector in a
flip-chip assembly. The vapor deposition of solder on the LED chip
then naturally has to be performed not on the back side of the
chip, but on the active epitaxial layer sequence of the LED
chip.
[0048] The connector can be enveloped by the plastic of the plastic
encapsulant on two main surfaces, so that no further heat sink is
present on the connector.
[0049] In addition to its use with radiation-emitting semiconductor
chips, the method according to the invention is also, of course,
applicable to the soldering of other semiconductor structures such
as, in particular, infrared sensors or infrared radiators, as well
as transistors.
* * * * *